(a) Field of the Invention
The present invention is related to an optical diffusion device, and more particularly, to one applied in a backlight module to effectively distribute streams of light from light source for increasing luminance of the entire backlight module.
(b) Description of the Prior Art
A backlight module is generally referred to a component that provides a back light source to a product and is currently applied in various types of information, communication, and consumer products, e.g., liquid crystal displays (LCD), negative scanners, sliders, or light panels for slides. Depending on the location of the light from its source to enter, the backlight module is available in edge lighting and bottom lighting. The edge lighting backlight module is usually applied in products, e.g., portable computers that require power-saving and that are thinner and lighter in construction. To meet the requirements, a light source is usually provided on an edge of the backlight module, and a light guide plate is disposed to guide streams of light emitted from the light source to a display panel.
The bottom light backlight module is usually applied in a product that requires higher brightness, e.g. a TV set. As illustrated in FIG. 1, a bottom light backlight module 1 is comprised of a frame 11. A reflective coating is applied or a reflection film 12 is attached on an inner side of the frame 11. Multiple light sources 13 are arranged and spaced at intervals in sequence. A diffuser 14 is disposed over those light sources 13. One or a plurality of optical diffusion films 15 and one or a plurality of brightness enhancing films (BEF) 16 are disposed on the diffuser 14. Finally, a display panel 17 is placed on top of the BEF to form a TFT-LCD.
Although the purpose of the optical diffusion device including the diffuser or diffusion film is only to permit uniform diffusion of the light passing through, it improves a phenomenon of dim and dark regions found with the liquid crystal module. Therefore, an improvement attempted to narrow down the dim and dark regions by extending a gap between those light sources 13 and the diffuser 14 for admitting more streams of light emitted from those light sources 13 into the diffuser 14. However, the structural design of the improvement for providing limited effect and causing the backlight module to get thicker defies the purpose of having a compact design for the liquid crystal module.
There are two types of processes for manufacturing an optical diffusion device. One process involves formation of microstructures for diffusion on a surface of a substrate, and another process is to coat micro-particles on the surface of the substrate or mix them in the substrate. The process of coating those micro-particles usually fails to provide high uniformity and high yield. The limited number of micro-particles to be coated fails to upgrade diffusion efficiency. Also, the micro-particles could easily scratch other devices. The diffusion efficiency may be upgraded by mixing those micro-particles with the substrate, but the light permeability remains low.
The microstructure formed on the surface of the substrate indicates either an irregularly fluctuating frosted glass structure or a regular lens array. The frosted glass type of structure was earlier used in the light diffusion structure. However, its diffusion rate is low, and its diffusion direction is random, thereby failing to provide diffusion in a given direction for a device including a fluorescent tube. A cylindrical lens array effectively controls diffusion direction and is currently designed in a form of a continuous arc, a sine wave, a triangle, or a square. The lens array is applied in a bottom lighting backlight module 1 in an LCD as disclosed in US2003/0184993A1 and Japanese 2000-75102. The former applies the lens array in a bottom lighting backlight module 1 in an LCD to achieve diffusion effect, and the latter applies a sine wave lens array in a collector. The design of continuous arcs, each with greater than a semicircle, achieves the best optical diffusion. As illustrated in FIGS. 2(A) and 2(B), multiple cylindrical lenses 18, each in a sine wave form or any other form, however, fail to deliver uniform diffusion of streams of light emitted from the light source (the arrow indicates the incident beams). Therefore, those optical diffusion devices fail to solve the problem of dim and dark regions found with a backlight module of the prior art.